Combined thermal and high pressure colour degradation of tomato puree and strawberry juice

Visual colour degradation of tomato puree and strawberry juice at three different pH values (2.5, 3.7 and 5) during thermal (100–140 °C, 0–120 min) and high pressure thermal (300–700 MPa, 60 min, 65 °C) treatments were studied. Hunter colour scale values L∗, a∗ and b∗ of each treated sample were measured. Results indicated that the thermal degradation of tomato and strawberry colour followed first order kinetics (fractional conversion model). The L∗a∗/b∗ parameter combination described best the colour change of all samples. The activation energies for the different material were 129.12, 181.40, 162.60, 85.77 kJ/mol × 10−2 for tomato puree, strawberry at pH 2.5, strawberry at pH 3.7, and strawberry at pH 5, respectively. Colour of strawberry at pH 5 was less heat stable but the degradation constants were less sensitive to temperature changes.No colour degradation of tomato appeared under combined thermal and high pressure treatment; a maximum increase of 8.8% in L∗a∗/b∗ parameter was found for strawberry samples (pH 5).